Under-Sink Water Filters: Aquaphor Crystal Flow Filtration Systems for Clean Drinking Water at Home – 2025 Guide

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In today’s world, drinking water quality raises increasing concerns. Even water that meets basic standards requires additional purification for your safety and comfort. In this article, we’ll examine in detail flow-through filters for under-sink installation, their features, and advantages.

The article examines and compares various types of household flow-type drinking water filters for installation under the kitchen sink or counter, their differences, and their advantages.

In one of the previous articles we showcased different reverse osmosis filtering systems, which have the most perfect degree of purification (about 99.9%). Now we will examine flow-through filtration systems – simple, but quite effective.

Great news! In 2024, Aquaphor released an updated Crystal filter line with improved characteristics and new technologies! Learn more about the new products, in a new interesting article !

Flow Filters vs Reverse Osmosis Systems: What to Choose?

Reverse Osmosis System Features:

• Maximum purification level (about 99.9%)
• Require preliminary filtration and high system pressure
• For 1 liter of purified water, 3-4 liters are drained
• Slow purification process usually requiring a storage tank

Flow Filter Advantages:

• No water drainage — all incoming water is purified
• Work with a wider pressure range
• Easier to install and maintain
• Effectively remove chlorine, heavy metals, pesticides, phenol, colloidal iron, microplastics
• Improve taste and odor thanks to activated carbon

Main Differences Between Flow Filters

By number of purification stages:

Three-stage filters are most common:

1. First filter — mechanical purification from solid impurities (polypropylene)
2. Second filter — selected based on source water characteristics
3. Third filter — usually a fine carbon block to eliminate foreign odors and tastes

By design:

Classic filtration systems:

• A series of sequentially connected containers
• Use standard size replacement filters (usually 2.5″x10″)
• Complex filter replacement — need to unscrew the housings

Modern compact systems:

• Fast filter element replacement technology
• Aquaphor developed patented Click-And-Turn and Push-and-Turn technology for maximum convenience
• Minimal time and effort required for maintenance

Advantages of Aquaphor Crystal Filters

Innovative technologies:

• Extended filter element service life
• Filtration of 6,000-8,000 liters of water before replacement
• Carbon-Fiber-Block (CFB) modules made from natural coconut carbon
• Aqualen ion exchange fiber for stabilizing capillary thickness
• The contact area between water and sorbents is 42 times larger than conventional filters
• Filtration speed is 4 times higher than standard
• Push-And-Turn one-hand fast and easy cartridge replacement

Ease of use:

• Simple filter replacement with Click-And-Turn and Push-and-Turn technology
• Cartridges replaced with housings — no special tools required
• No need to disassemble, rinse, and disinfect housings
• No contact with contaminated filter surfaces
• Compact monoblock takes minimal space under the sink

Aquaphor Crystal Filter Line Models

Popular models:

• Aquaphor Crystal — universal system for a wide range of applications
• Aquaphor Crystal H — system with softening cartridge K4 (KH) for hard water
• Aquaphor Crystal A — economical filter for urban tap water purification
• Aquaphor Crystal HA — variation of Crystal A system with softening cartridge
• Aquaphor Crystal ECO — variation of Crystal system with K7B cartridge (0.1 micron porosity) for protection against bacteria and large viruses

Comparison of cartridges in Aquaphor Crystal systems:

Aquaphor Crystal Cartridge Specifications

K3 — first purification stage:

• Carbon-fiber block (CFB)
• Sorption purification and mechanical filtration of particles larger than 10 microns
• Silver in active ionic form for bacteriostatic effect

K5 — first purification stage:

• Mechanical filter made of food-grade polypropylene
• 5 micron porosity
• Cleans from rust, sand, and silt

K2 — second purification stage:

• Carbon-fiber block (CFB)
• Deep sorption purification and mechanical filtration of particles larger than 3 microns
• Removes harmful impurities, including suspended matter, chlorine, heavy metals

KH (K4) — second purification stage (softening):

• Softens hard water
• Solves problems of scale and flakes in boiled water
• Can be regenerated at home with table salt

K7B — second or third purification stage:

• Two components in one housing
• Carbon-fiber block (CFB) and hollow fiber membrane
• Traps microparticles larger than 0.1 microns
• Protection against bacteria

K7 — third purification stage:

• Super-dense carbon block made of natural activated coconut carbon
• Final cleaning with 0.8 micron porosity
• Completely removes even the smallest amounts of harmful impurities

How to Choose the Right Flow Filter for Drinking Water?

Filter selection depends on your tap water quality:

• For generally safe water with minor issues (sand, traces of rust, chlorine odor) — Crystal or Crystal A
• For hard water with white residue after boiling — Crystal H or Crystal HA
• If bacteria are suspected — ultrafiltration system Crystal ECO or K7B cartridge installed in normal Crystal

We also recommend focusing on the taste and properties of filtered water. With Crystal filters, you can change the filter set at any time to find the optimal option.

Recommendations for Using Flow Filters

• With high initial water hardness (more than 7 meq/l), a slightly salty taste may appear after softening — this is normal
• If you haven’t used the filter for more than a week, run water through it for at least 5 minutes
• After installing new cartridges, be sure to flush the system (usually at least 20 minutes)
• If you doubt the bacterial safety of the source water, use antibacterial ultrafiltration cartridge K7B and/or boil the filtered water
• Use only freshly filtered water. Small quantities can be stored in the refrigerator for 1-2 days
• Protect filters from impacts, drops, and water freezing in them

Where to Buy Aquaphor Crystal Under-sink Water Filtration System?

Aquaphor’s main factories are located in Europe and the USA. The European market primarily receives products from the new production plant in Estonia, manufactured to the highest quality standards and complying with all EU regulations.

Buy Aquaphor Crystal filters in our online store ProMarket-EU

For wholesale orders: email ProMarket for wholesale discounts and special offers.
Special offer for a plumber
Special offer for a hardware store
Special offer for a pharmacy

Frequently asked questions from buyers and users of Aquaphor Crystal water purifiers (FAQ).

Photos and technical details courtesy of Aquaphor, ProMarket.

Other helpful information:
If you own a related business (for example, a store selling household goods and appliances, a pharmacy, or a plumbing company), you can offer your customers a new high-quality, profitable product.
Please email ProMarket for wholesale discounts and sales representative offers.

Special offer for a plumber
Special offer for a hardware store
Special offer for a pharmacy

RELEVANT VIDEOS

First unboxing of Aquaphor Crystal A new version 2024:

Video instructions for installing a series Crystal of water purifiers under the sink:

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This post is also available in: English Italiano (Italian)